Endothelium-derived Nitric Oxide Research Articles

Effect of nebivolol on beat-to-beat and short-term blood pressure variability in spontaneously hypertensive rats

Cardiovascular effects and pharmacokinetics of nebivolol were assessed in spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) animals. Male SH and WKY rats were treated with vehicle or nebivolol 0.3, 3, or 10 mg kg(-1) (i.v.) and effects on blood pressure (BP), heart rate, and blood pressure variability (BPV) were recorded. Plasma pharmacokinetics of d- and l-nebivolol was studied by traditional blood sampling. Short-term and beat-to-beat BPV was assessed by standard deviation and spectral analysis of BP recording, respectively. Nebivolol showed enantioselective pharmacokinetics in both experimental groups; clearance of l-nebivolol was significantly greater than d-enantiomer. Clearance of nebivolol was significantly reduced in SHR with regards to WKY animals. Hypotensive response to nebivolol 3 and 10 mg kg(-1) was significantly enhanced in SHR compared with normotensive animals. Spectral analysis of beat-to-beat BPV showed a greater reduction in low frequency BPV in SHR than in WKY rats. Nebivolol 3 and 10 mg kg(-1) significantly reduced ratio low frequency/high frequency BPV only in SHR. Short-term BPV was markedly reduced by nebivolol 0.3, 3, and 10 mg kg(-1) in WKY and SHR. In conclusion, the hypertensive stage in SHR modifies nebivolol pharmacokinetic properties and enhances its hypotensive response due to a greater attenuation in vascular sympathetic activity and enhancement of endothelial-derived NO activity. Nebivolol markedly attenuates short-term BPV in both experimental groups providing beneficial cardiovascular effects by both controlling high blood pressure and its short-term variability.

Platelet Ca2+ responses coupled to glycoprotein VI and Toll-like receptors persist in the presence of endothelial-derived inhibitors: roles for secondary activation of P2X1 receptors and release from intracellular Ca2+ stores

AbstractInhibition of Ca2+ mobilization by cyclic nucleotides is central to the mechanism whereby endothelial-derived prostacyclin and nitric oxide limit platelet activation in the intact circulation. However, we show that ∼ 50% of the Ca2+ response after stimulation of glycoprotein VI (GPVI) by collagen, or of Toll-like 2/1 receptors by Pam3Cys-Ser-(Lys)4 (Pam3CSK4), is resistant to prostacyclin. At low agonist concentrations, the prostacyclin-resistant Ca2+ response was predominantly because of P2X1 receptors activated by ATP release via a phospholipase-C–coupled secretory pathway requiring both protein kinase C and cytosolic Ca2+ elevation. At higher agonist concentrations, an additional pathway was observed because of intracellular Ca2+ release that also depended on activation of phospholipase C and, for TLR 2/1, PI3-kinase. Secondary activation of P2X1-dependent Ca2+ influx also persisted in the presence of nitric oxide, delivered from spermine NONOate, or increased ectonucleotidase levels (apyrase). Surprisingly, apyrase was more effective than prostacyclin and NO at limiting secondary P2X1 activation. Dilution of platelets reduced the average extracellular ATP level without affecting the percentage contribution of P2X1 receptors to collagen-evoked Ca2+ responses, indicating a highly efficient activation mechanism by local ATP. In conclusion, platelets possess inhibitor-resistant Ca2+ mobilization pathways, including P2X1 receptors, that may be particularly important during early thrombotic or immune-dependent platelet activation.

Upregulation of endothelium-derived hyperpolarizing factor compensates for the loss of nitric oxide in mesenteric arteries of dahl salt-sensitive hypertensive rats

This study was designed to determine whether a high-salt diet would alter endothelial function and, if so, the relative contributions of endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide (NO) to any changes in vasomotor responses. Male Dahl salt-sensitive (DS) rats were given either a high-salt diet (8% NaCl, DS-H) or a low-salt diet (0.4% NaCl, DS-L) for 6 weeks. Membrane potentials and contractile responses were recorded from the isolated superior mesenteric arteries. After salt loading, DS-H developed hypertension, while DS-L remained normotensive. No difference was found in acetylcholine (ACh)-induced, endothelium-dependent relaxation between the groups. However, after treatment with indomethacin and NO synthase inhibitor, EDHF-like relaxation was significantly greater in DS-H than in DS-L. In contrast, NO-mediated relaxation was significantly smaller in DS-Hthan in DS-L. Iberiotoxin (IbTx), a specific blocker of large-conductance calcium-dependent potassium (BKCa) channels, attenuated EDHF-like relaxation in DS-H but not in DS-L. IbTx marginally inhibited EDHF-mediated hyperpolarization only in DS-H. Endothelium-independent relaxation in response to sodium nitroprusside or levcromakalim was similar in both groups. In conclusion, EDHF-like relaxation is upregulated through the activation of BKCa channels in the mesenteric arteries of DS-H. As the overall relaxation in response to ACh did not differ between the groups, the upregulation of EDHF appears to compensate for the loss of NO in the mesenteric arteries of DS-H.

Effects of NADPH oxidase inhibitor apocynin on real‐time blood hydrogen peroxide release in femoral artery/vein ischemia and reperfusion

Vascular endothelial dysfunction can initiate oxidative stress during ischemia/reperfusion (I/R). Endothelial dysfunction is characterized by an increase in blood hydrogen peroxide (H2O2) and a decrease in endothelial‐derived nitric oxide (NO) bioavailability. Previous studies using Gö 6983, a broad‐spectrum protein kinase C inhibitor that can inhibit NADPH oxidase activity, has attenuated blood H2O2 levels during femoral I/R in vivo. This study examines the effects of apocynin, a direct NADPH oxidase inhibitor, on real‐time blood H2O2 levels in femoral I/R in vivo. H2O2 microsensors (100 μm) were inserted into both femoral veins in anesthetized rats. One hind limb was subjected to ischemia by clamping the femoral artery and vein for 20 minutes and allowed to reperfuse for 45 minutes, while the other hind limb served as a sham. In the control group, H2O2 was significantly increased by 1.3–2.7 μM during 45 minutes of reperfusion in the I/R vein when compared to the sham vein (n=4, P<0.05). Intravenous apocynin (13.7 mg/kg) given at the beginning of reperfusion significantly decreased blood H2O2 levels compared to the control group (n=6, P<0.05). The data suggests that apocynin attenuates oxidative stress in femoral I/R, which may be due to inhibition of leukocyte/endothelial NADPH oxidase.

Pitavastatin Improves Endothelial Function and Glucose Metabolism in Ovariectomized Mice

Estrogen deficiency increases the cardiovascular risks and metabolic dysfunction in postmenopausal women. The potential effects of estrogen are partially related to its direct effects on the vascular wall, stimulating endotheliumderived NO synthesis (eNOS). HMG-CoA reductase inhibitors (statins) may also improve the endothelial function through upregulation of eNOS. In this study, we examined whether the treatment of pitavastatin for a short period (1 week) may improve the endothelial function or glucose metabolism under estrogen deficiency induced by ovariectmy. At 4 weeks after ovariectomy, hyperglycemia and hyperinsulinemia were observed in estrogen deficient mice as assessed by intraperitoneal glucose tolerance test, and endothelial dysfunction was also observed as assessed by the vasodilator response to acetylcholine. At 3 weeks after ovariectomy, we started to administer pitavastatin to ovariectomized mice for 1 week. Although the treatment of pitavastatin for a week did not affect obesity, the treatment of pitavastatin significantly attenutaed hyperglycemia and hyperinsulinemia as well as endothelial dysfunction induced by estrogen deficiency. These results demonstrated that treatment of pitavastatin rapidly improved glucose metabolism and endothelial function under estrogen deficiency. Keywords: Endothelial function, eNOS, estrogen, hyperglycemia, hyperinsulinemia, insulin resistance, IGF-1, menopause, ovariectomy, statins

Effect of chronic sodium nitrite therapy on monocrotaline-induced pulmonary hypertension

Pulmonary hypertension (PH) is a rare disorder that without treatment is progressive and often fatal within 3years. The treatment of PH involves the use of a diverse group of drugs and lung transplantation. Although nitrite was once thought to be an inactive metabolite of endothelial-derived nitric oxide (NO), there is increasing evidence that nitrite may be useful in the treatment of PH, but the mechanism by which nitrite exerts its beneficial effect remains uncertain. The purpose of this study was to investigate the effect of chronic sodium nitrite treatment in a PH model in the rat. Following induction of PH with a single injection of monocrotaline, 60mg; daily ip injections of sodium nitrite (3mg/kg) starting on day 14 and continuing for 21days, resulted in a significantly lower pulmonary arterial pressure on day 35 when compared to values in untreated animals with monocrotaline-induced PH. In monocrotaline-treated rats, daily treatment with ip nitrite injections for 21days decreased right ventricular mass and pathologic changes in small pulmonary arteries. Nitrite therapy did not change systemic arterial pressure or cardiac output when values were measured on day 35. The decreases in pulmonary arterial pressure in response to iv injections of sodium nitroprusside, sodium nitrite, and BAY 41-8543 were not different in rats with monocrotaline-induced pulmonary hypertension and rats with chronic nitrite therapy when compared to responses in animals in which pulmonary arterial pressure was increased with U46619. These findings are consistent with the hypothesis that the mechanisms that convert nitrite to vasoactive NO, activate soluble guanylyl cyclase and mediate the vasodilator response to NO or an NO derivative are not impaired. The present data are consistent with the results of a previous study in monocrotaline-induced PH in which systemic arterial pressure and cardiac output were not evaluated and are consistent with the hypothesis that nitrite is effective in the treatment of monocrotaline-induced PH in the rodent.

Nitric oxide signaling in hypoxia

Endothelial-derived nitric oxide (NO) is classically viewed as a regulator of vasomotor tone. NO plays an important role in regulating O(2) delivery through paracrine control of vasomotor tone locally and cardiovascular and respiratory responses centrally. Very soon after the cloning and functional characterization of the endothelial nitric oxide synthase (eNOS), studies on the interaction between O(2) and NO made the paradoxical finding that hypoxia led to decreases in eNOS expression and function. Why would decreases in O(2) content in tissues elicit a loss of a potent endothelial-derived vasodilator? We now know that restricting our view of NO as a regulator of vasomotor tone or blood pressure limited deeper levels of mechanistic insight. Exciting new studies indicate that functional interactions between NO and O(2) exhibit profound complexity and are relevant to diseases states, especially those associated with hypoxia in tissues. NOS isoforms catalytically require O(2). Hypoxia regulates steady-state expression of the mRNA and protein abundance of the NOS enzymes. Animals genetically deficient in NOS isoforms have perturbations in their ability to adapt to changes in O(2) supply or demand. Most interestingly, the intracellular pathways for O(2) sensing that evolved to ensure an appropriate balance of O(2) delivery and utilization intersect with NO signaling networks. Recent studies demonstrate that hypoxia-inducible factor (HIF) stabilization and transcriptional activity is achieved through two parallel pathways: (1) a decrease in O(2)-dependent prolyl hydroxylation of HIF and (2) S-nitrosylation of HIF pathway components. Recent findings support a role for S-nitrosothiols as hypoxia-mimetics in certain biological and/or disease settings, such as living at high altitude, exposure to small molecules that can bind NO, or anemia.

Abstract 3663: Characterization of Cerebrovascular Parameters using MRI in Endothelial Nitric Oxide Synthase Knockout Mice

Endothelial-derived nitric oxide (NO) is important for properly regulating vascular tone and maintaining blood pressure. Mice lacking endothelial NO synthase (eNOS), i.e. loss of endothelial NO production, have systemic hypertension and develop larger cerebral infarction upon cerebral ischemia. Given that constitutively produced NO is necessary for a normal endothelial function, we posit that cerebrovascular characters in eNOS KO mice brain may differ in structure and physiology. In this study, we aim to establish MRI-derived vascular parameters such as cerebral blood volume (CBV), water exchange index (WEI), and vessel size index (VSI) using two different MRI intravascular contrast agents (Gd-PGC (Protected graft copolymer bearing covalently linked Gd- DTPA residues) and SPION (superparamagnetic iron oxide nanoparticle)). We also investigated whether perivascular aquaporine (AQP) proteins, which play a central role in the pathophysiology of many diseases, are differently expressed in eNOS KO mice. Flip angle dependence of the MRI signal intensity on transvascular water exchange rate was used to quantify CBV and WEI before and after intravenous administration of Gd-PGC using wild type mice (C57BL/6, n=8) and eNOS KO mice (n=5). 2D T2 and T2* maps were also acquired before and after SPION administration for measurements of cerebral VSI. As results, eNOS KO mice have lower VSI than that that in wild type mice ( Fig. A ). The CBV of eNOS KO mice is not significantly different from that of wild type mice ( Fig. B ). Furthermore, baseline WEI significantly increased in the eNOS KO mice, indicating higher BBB water permeability. However, both AQP1 and AQP4 were less expressed in eNOS KO mice than those in wild type mice ( Fig. D ). These suggest that the loss of eNOS contribute to the decrease of the vessel diameter and increase of water permeability under a baseline physiological condition. However, expression of AQP proteins forming vascular water channels is not involved with the observed water exchange rate increase across the BBB in eNOS KO mice. The study warrants future investigations to elucidate the relationship between NO synthase and the BBB integrity and its involvement with ischemic damage.

Simulation of NO and O2 transport facilitated by polymerized hemoglobin solutions in an arteriole that takes into account wall shear stress-induced NO production

A mathematical model was developed to study nitric oxide (NO) and oxygen (O2) transport in an arteriole and surrounding tissues exposed to a mixture of red blood cells (RBCs) and hemoglobin (Hb)-based O2 carriers (HBOCs). A unique feature of this model is the inclusion of blood vessel wall shear stress-induced production of endothelial-derived NO, which is very sensitive to the viscosity of the RBC and HBOC mixture traversing the blood vessel lumen. Therefore in this study, a series of polymerized bovine Hb (PolyHb) solutions with high viscosity, varying O2 affinities, NO dioxygenation rate constants and O2 dissociation rate constants that were previously synthesized and characterized by our group was evaluated via mathematical modeling, in order to investigate the effect of these biophysical properties on the transport of NO and O2 in an arteriole and its surrounding tissues subjected to anemia with the commercial HBOC Oxyglobin® and cell-free bovine Hb (bHb) serving as appropriate controls. The computer simulation results indicated that transfusion of high viscosity PolyHb solutions promoted blood vessel wall shear stress dependent generation of the vasodilator NO, especially in the blood vessel wall and should transport enough NO inside the smooth muscle layer to activate vasodilation compared to the commercial HBOC Oxyglobin® and cell-free bHb. However, NO scavenging in the arteriole lumen was unavoidable due to the intrinsic high NO dioxygenation rate constant of the HBOCs being studied. This study also observed that all PolyHbs could potentially improve tissue oxygenation under hypoxic conditions, while low O2 affinity PolyHbs were more effective in oxygenating tissues under normoxic conditions compared with high O2 affinity PolyHbs. In addition, all ultrahigh molecular weight PolyHbs displayed higher O2 transfer rates than the commercial HBOC Oxyglobin® and cell-free bHb. Therefore, these results suggest that ultrahigh molecular weight PolyHb solutions could be used as safe and efficacious O2 carriers for use in transfusion medicine. It also suggests that future generations of PolyHb solutions should possess lower NO dioxygenation reaction rate constants in order to reduce NO scavenging, while maintaining high solution viscosity to take advantage of wall shear stress-induced NO production. Taken together, we suggest that this mathematical model can be used to predict the vasoactivity of HBOCs and help guide the design and optimization of the next generation of HBOCs for use in transfusion medicine.

Intermedin elicits a negative inotropic effect in rat papillary muscles mediated by endothelial-derived nitric oxide

Intermedin (IMD) is a novel vasoactive peptide from the calcitonin gene-related peptide (CGRP) implicated in cardiac regulation, yet the contractile effects of IMD remain controversial, since previous studies in vivo and isolated cardiomyocytes documented contradictory results. We hypothesized cardiac endothelial cells involvement in IMD modulation of cardiac function as an explanation for these opposing observations. With this in mind, we investigated the direct action of increasing concentrations of IMD (10(-8) to 10(-6)M) on myocardial performance parameters in rat left ventricular (LV) papillary muscles with and without endocardial endothelium (EE) and in presence of receptor antagonists and intracellular pathways inhibitors. In LV papillary muscles with intact EE, IMD induced a concentration-dependent negative inotropic action (%decrease relative to baseline, at IMD concentration of 10(-6)M, active tension of 14 ± 4%, and maximum velocity of tension rise of 10 ± 4%). These effects were blunted by EE removal, AM receptor antagonist (AM(22-52)), and CGRP receptor antagonist (CGRP(8-37)). Additionally, nitric oxide (NO) synthase inhibition with N(G)-nitro-l-arginine (l-NAME) in muscles with and without EE and guanylyl cyclase inhibition with {1H-[1,2,4]oxadiazole-[4,4-a]-quinoxalin-1-one} not only blunted the negative inotropic action of IMD but also unmasked IMD-positive inotropic effect dependent on CGRP receptor PKA activation. Western blot quantification of phosphorylated cardiac troponin I (P-cTnI) in IMD-treated papillary muscles revealed a significant increase in P-cTnI when compared with untreated muscles, while in l-NAME-pretreated papillary muscles IMD failed to increase P-cTnI. Finally, we found that stimulation of both EE and microvascular endothelial cells with IMD significantly increased NO production by 40 ± 3 and 38 ± 3%, respectively, suggesting the role of cardiac endothelial cells in NO production upon IMD stimulation. Our findings establish IMD negative inotropic effect in isolated myocardium due to NO/cGMP pathway activation with concomitant thin myofilament desensitization by increase in cTnI phosphorylation and provide a coherent explanation for the previously reported contradictory results.

Regulation and Maintenance of Vascular Tone and Patency in Cardiovascular Health and Disease

Despite numerous advances in health care practices, cardiovascular disease still remains the leading cause of morbidity and mortality worldwide. Perhaps the most important consequence of cardiovascular disease is the interruption of blood flow to organs such as the heart and brain, resulting in the clinical presentation of a heart attack or stroke. As such, the regulation of vascular tone and the maintenance of vascular patency are vital for the preservation of cardiovascular health. Central to this process is the vascular endothelium. The endothelium is vital for the regulation of vascular tone and the maintenance of vascular homeostasis, as it releases factors such as nitric oxide, hydrogen sulfide, endothelial-dependent hyperpolarizing factor, and prostacyclin that induce vasodilatation and keep the vasculature free of obstructions [1]. Therefore, it should be of no surprise that a number of the risk factors for the development of cardiovascular disease, such as hypertension, hypercholesterolemia, diabetes, smoking, ageing, and atherosclerosis, correlate with an impaired endothelium [2]. This impairment, termed endothelial dysfunction, is characterized by the reduction in the bioavailability of vasodilators, particularly nitric oxide, and/or an increase in endothelium-derived contracting factors [3]. The resulting imbalance leads to an impairment of endothelium-dependent vasodilation, as well as a compromised state of endothelial activation characterized by proinflammatory, proliferative, and procoagulatory conditions that favor all stages of atherogenesis [4]. Therefore, it is critically important to develop and implement therapeutic strategies that will combat endothelial dysfunction in an effort to reduce the mortality and morbidity associated with cardiovascular diseases. However, before therapeutic strategies can be implemented it is important to have a clear understanding of the pathological mechanisms that lead to the endothelial dysfunction in the first place. This special issue of highlights the latest findings related to the role of endothelial dysfunction in cardiovascular disease and comprises five review articles and one original report. The first three articles share the common theme of endothelial dysfunction in diabetes. Each paper offers unique insights into the mechanisms underlying diabetes-induced changes in endothelial biology and highlights specific pathways that could be novel therapeutic targets. The review article in this series by S. D. Funk et al. discusses the mechanisms that contribute to the development of atherosclerosis in diabetics. This paper highlights the central role of hyperglycemia in promoting endothelial dysfunction and discusses how cellular and animal studies have translated to clinical development of therapeutics targeting endothelial dysfunction in diabetes. The next paper by A. Sharma et al. highlights the importance of alterations in endothelium-derived nitric oxide (EDNO) production in the pathogenesis of vascular complications in both type 1 and type 2 diabetes. The interrelationship between reactive oxygen species (ROS) and EDNO is described, with emphasis on the cellular and molecular mechanisms that give rise to altered NO bioavailability in diabetes. In their paper, G. K. Kolluru et al. emphasize the importance of angiogenesis in diabetes and chronicle studies that have yielded mechanistic insights into the development of endothelial dysfunction in diabetes. This comprehensive paper, entitled “Endothelial dysfunction and diabetes: effects on angiogenesis, vascular remodeling, and wound healing,” discusses how ROS and deficiencies in NO bioavailability contribute to altered angiogenesis in diabetes. Therapeutic management of angiogenesis in diabetes is also discussed. In another review article in this series, M. Murakami provides a comprehensive overview of the mechanisms contributing to the active maintenance of the vasculature. The role of growth factors and cytokines in mediating endothelial and mural cell maintenance is described, with an analysis of how genetic alterations in these pathways give rise to blood vessel abnormalities and susceptibility to vascular disease. The molecular and cellular mechanisms leading to restenosis and the potential for new therapeutics targeting vascular smooth muscle cell (VSMC) proliferation are the topic of a review article in this series. L. Denes et al. highlight the importance of VSMC phenotype switching and proliferation in vascular disease and discuss the clinical diagnosis and management of restenosis. The original report by I. Liesmaa et al. is entitled “Bradykinin type-2 receptor expression correlates with age and is subjected to transcriptional regulation.” This study demonstrates that bradykinin type-2 receptor (BK-2R) mRNA is positively correlated with age, but is significantly reduced in human patients with idiopathic dilated cardiomyopathy (IDC) compared with healthy individuals. The study further examines the relationship between polymorphisms in the BK-2R promoter and the presence of IDC and coronary heart disease.

Expression of endothelial nitric oxide synthase in blood vessels and silicic acid consumption

NO produces by endothelial nitric oxide synthase (eNOS) represents one of the most representative vasoactive molecules able to regulate vascular tone; it is released by endothelial cells and it diffuses to adjacent vascular smooth muscle cells causing vasorelaxation. In addition, endothelium-derived NO is know to be involved in multiple ways to prevent the progression of age-related vascular diseases. Senescent endothelial cells are characterized by a decreased production of endothelium-derived NO due to a decrease of eNOS activity that could be attributable to a reduction in eNOS protein expression as well as in eNOS phosphorylation (Matsushita et al., 2001). Previous studies showed that silicon, mainly as silicic acid, plays an important role as protective factor against the development of age-related vascular diseases, maintaining integrity, stability and elastic properties of arterial walls (Schwarz et al., 1977). So, the aim of this study was to evaluate the relationship between the expression of eNOS and silicic acid consumption in a mouse model of early physiological aging. We evaluated qualitatively and quantitatively by immunohistochemical method, the expression of eNOS in the vessel wall of aorta and renal vessels in relation with the administration of silicic acid in drinking water. The results showed that loss of eNOS expression was prevented by regular consumption of silicic acid rich water, supporting the potential protective role of silicon against age related-vascular disorders.

Vascular Aging in Women: is Estrogen the Fountain of Youth?

Aging is associated with structural and functional changes in the vasculature, including endothelial dysfunction, arterial stiffening and remodeling, impaired angiogenesis, and defective vascular repair, and with increased prevalence of atherosclerosis. Cardiovascular risk is similar for older men and women, but lower in women during their fertile years. This age- and sex-related difference points to estrogen as a protective factor because menopause is marked by the loss of endogenous estrogen production. Experimental and some clinical studies have attributed most of the protective effects of estrogen to its modulatory action on vascular endothelium. Estrogen promotes endothelial-derived NO production through increased expression and activity of endothelial nitric oxide synthase, and modulates prostacyclin and thromboxane A2 release. The thromboxane A2 pathway is key to regulating vascular tone in females. Despite all the experimental evidence, some clinical trials have reported no cardiovascular benefit from estrogen replacement therapy in older postmenopausal women. The “Timing Hypothesis,” which states that estrogen-mediated vascular benefits occur only before the detrimental effects of aging are established in the vasculature, offers a possible explanation for these discrepancies. Nevertheless, a gap remains in current knowledge of cardiovascular aging mechanisms in women. This review comprises clinical and experimental data on the effects of aging, estrogens, and hormone replacement therapy on vascular function of females. We aim to clarify how menopause and aging contribute jointly to vascular aging and how estrogen modulates vascular response at different ages.

Letter to the Editor Obstructive sleep apnoea syndrome and cardiovascular risk

Zamarron et al. [1] report that obstructive sleep apnoea syndrome (OSAS) is associated with raised levels of markers of endothelial function. Moreover, some of these markers (intercellular cell adhesion molecule-1 (ICAM-1) and plasminogen activator inhibitor-1 (PAI-1)) improved after nasal continuous positive airway pressure [1]. Some additional comments may be of interest. Metabolic syndrome (MetS) is highly prevalent in patients with OSAS [2]. In turn, intermittent hypoxia increases insulin resistance [2]. Consequently, it is difficult to identify the contribution of OSAS and MetS to vascular risk, since they share common predisposing factors (e.g. obesity [2] and endothelial dysfunction [3]). Markers of endothelial activation, including ICAM-1, PAI-1 and E-selectin, are raised in MetS [3] and Zamarron et al. [1] report a similar pattern in OSAS. Platelet activation occurs in MetS due to reduced availability of endothelium-derived nitric oxide (NO) and prostacyclin [4]. Similarly, in OSAS a decrease in NO availability and prostacyclin/thromboxane metabolite ratio has been reported [2, 5]. Markers of platelet activation, including mean platelet volume (MPV) and platelet distribution width (PDW), were increased in OSAS, in parallel with the severity of hypoxia [6]. Therefore, it would be helpful to know how many patients in the control and OSAS group had MetS in the Zamarron et al. [1] study. Taken together, all these findings highlight the role of OSAS on endothelial integrity and as a contributor to cardiovascular risk.

Regulation of Coronary Vasomotor Function by Reactive Oxygen Species

Overproduction of reactive oxygen species is closely associated with cardiovascular diseases in part by impairing endothelial function and consequently compromising blood flow regulation. Superoxide and hydrogen peroxide are elevated under various disease states with reduced endothelium-derived nitric oxide bioavailability. The oxidative stress elicited by angiotensin II, C-reactive protein and tumor necrosis factor-α is mediated by the activation of different redox signaling pathways in the microvasculature. The upregulation of L-arginine consuming enzyme arginase also contributes to the reduced nitric oxide bioavailability during oxidative stress. Hydrogen peroxide exhibits vasodilator function in the coronary microcirculation and plays an important role in the physiological regulation of coronary blood flow. However, excessive production of hydrogen peroxide impairs endothelial function by reducing L-arginine availability through hydroxyl radical-mediated upregulation of arginase. This review summarizes the current knowledge on the effects superoxide and hydrogen peroxide on vasomotor function regulated by the endothelium-derived nitric oxide and prostacyclin in the coronary microcirculation.

Sitting and endothelial dysfunction: the role of shear stress.

SummarySedentary activity is a modifiable life-style behavior and a key component in the etiology of atherosclerotic cardiovascular disease (ACVD). US adults and children spend more than half their waking time in sedentary pursuits. Sedentary activity has been shown to result in impaired insulin sensitivity, impaired metabolic function and attenuated endothelial function, which are classic markers of ACVD. Sedentary activity is defined as ‘sitting without otherwise being active.’ This behavior promotes reduced muscular activity of the lower extremities which decreases leg blood flow, increases blood pooling in the calf, augments mean arterial pressure, and deforms arterial segments resulting in low mean shear stress (SS). SS activates distinct physiological mechanisms which have been proposed to be protective against ACVD; specifically through a SS-induced endothelium-derived nitric oxide mechanism. Reduced bioavailability of nitric oxide creates a pro-oxidant milieu resulting in increased oxidative stress. There is sufficient evidence which demonstrates that endothelial function is attenuated in the presence of oxidative stress. Sedentary activity results in low SS in the lower extremities which may result in increased oxidative stress and impaired endothelial function. This review furthers the use of sitting as model to study the effects of inactivity, discusses possible physiological mechanisms and suggests future directions.

Cynanchum wilfordii ameliorates hypertension and endothelial dysfunction in rats fed with high fat/cholesterol diets

Hypercholesterolemia increases the incidence of atherosclerosis and its pathologic complications. This study was performed to test the effect of an ethanol extract of Cynanchum wilfordii (ECW) on vascular dysfunction in rats fed with high fat/cholesterol diets (HFCD). Male rats were fed a HFCD consisting of 7.5% cocoa butter and 1.25% cholesterol, with or without 100, 200 mg/day/kg ECW. Rats fed with HFCD increased body weight associated with an increase in plasma low-density lipoprotein (LDL) cholesterol level. Chronic ECW treatment in HFCD-fed rats lessened LDL cholesterol and triglyceride levels as well as elevated high-density lipoprotein (HDL) cholesterol. Chronic ECW treatment recovered the HFCD-induced increase in systolic blood pressure, maintained smooth and soft intima endothelial layers by the decrease of intima-media thickness. ECW significantly recovered the diet-induced decrease in vasorelaxation to acetylcholine, high-dose ECW apparently increased vasorelaxation response to sodium nitroprusside in rats fed with HFCD. ECW clearly restored the HFCD-induced reduction in endothelial nitric oxide (NO) synthase expression and Akt expression levels in aortic tissue, leading to improve endothelial function through an increase in endothelium-derived NO production. Furthermore, treatment of ECW significantly recovered the HFCD-induced decrease in aortic cGMP levels in rats. These findings suggest that ECW ameliorates hypertension and endothelial dysfunction via improvement of NO/cGMP signaling pathway in aortic tissue of rats fed with HFCD, suggesting a vascular protective role for this herb in the treatment and prevention of atherosclerotic vascular disease.

Darbepoetin enhances endothelium-dependent vasomotor function in patients with stable coronary artery disease only after preceding ischaemia/reperfusion

Vasoprotective effects of erythropoietin in animal models are mediated by endothelium-derived NO and/or mobilization of EPCs (endothelial progenitor cells) and may be enhanced by ischaemia: whether they are present in humans is unknown. We examined whether the erythropoietin analogue darbepoetin improves FMD (flow-mediated dilatation), a measure of endothelium-derived NO, and whether this is influenced by preceding I/R (ischaemia/reperfusion). A total of 36 patients (50-75 years) with stable coronary artery disease were randomized to receive a single dose of darbepoetin (300 μg) or saline placebo. FMD was measured at the brachial artery using high-resolution ultrasound. CD133⁺/CD34⁺/VEGFR2⁺ (vascular endothelial growth factor receptor 2) circulating EPCs were enumerated by flow cytometry. Measurements were made immediately before darbepoetin/placebo and at 24 h, 72 h and 7 days. At 24 h, FMD was repeated after 20 min of I/R of the upper limb. A further group of 11 patients was studied according to the same protocol, all receiving darbepoetin, with omission of forearm I/R at 24 h. Immunoreactive erythropoietin peaked at 24 h and remained elevated at approximately 50-fold of baseline at 72 h. FMD did not differ significantly between groups at 24 h (before I/R). At 72 h (48 h after I/R), FMD was greater (by 2.3±0.5% in the darbepoetin compared with the placebo group, a 66% increase over baseline; P<0.001) and greater than FMD at the same time point without preceding I/R (P<0.01). Increases in CD133⁺/CD34⁺/VEGFR2⁺ cells after darbepoetin did not differ according to the presence or absence of preceding I/R. Preceding I/R is required for darbepoetin to enhance endothelial function, possibly by increasing expression of the erythropoietin receptor and by a mechanism likely to involve Akt/NO rather than circulating EPCs.

The effect of cardiopulmonary bypass in coronary artery bypass surgeries (on-pump versus off-pump) on erectile function and endothelium-derived nitric oxide levels

To investigate the effects of on-pump and off-pump coronary artery bypass grafting (CABG) on the erectile function and endothelium-derived nitric oxide (eNO) levels. Twenty-eight consecutive patients were randomized into two groups depending on use of cardiopulmonary bypass in CABG surgery. The erectile function was evaluated by using the IIEF-5 questionnaire. The plasma eNO levels were determined at baseline and after reactive hyperemia before and after surgery. Blood was collected in one minute after cuff deflation from the radial artery on the same side. After CABG surgery the mean IIEF-5 score increased insignificantly over baseline from 14.8 to 15.8 (p = 0.29) and 12.4 to 14.3 (p = 0.11) after on-pump and off-pump CABG surgeries, respectively. The baseline plasma NO levels before surgery were 18.16 ± 7.63 nmol/L in on-pump and 21.76 ± 11.08 nmol/L in off-pump CABG. After reactive hyperemia the plasma NO levels were 22.14 ± 10.52 nmol/L in on-pump and 21.49 ± 9.13 nmol/L in off-pump CABG before the surgery. The difference in the plasma NO levels before surgery was not significant (p = 0.51). Two hours after surgery, the difference of the plasma NO levels at baseline (24.44 ± 12.31 on -pump and 20.58 ± 6.74 nmol/L off-pump CABG) and after reactive hyperemia (35.55 ± 23.54 nmol/L on-pump and 23.00 ± 15.40 nmol/L off-pump CABG) were not significantly different from each other (p = 0.11). Patients who had on-pump or off-pump CABG surgeries had higher IIEF-5 scores. Nevertheless, the improvement was insignificant in both groups. Meanwhile, on-pump or off-pump CABG surgeries did not have significant effect on plasma eNO levels.

Targeting Endothelial Dysfunction in Vascular Complications Associated with Diabetes

Cardiovascular complications associated with diabetes remain a significant health issue in westernized societies. Overwhelming evidence from clinical and laboratory investigations have demonstrated that these cardiovascular complications are initiated by a dysfunctional vascular endothelium. Indeed, endothelial dysfunction is one of the key events that occur during diabetes, leading to the acceleration of cardiovascular mortality and morbidity. In a diabetic milieu, endothelial dysfunction occurs as a result of attenuated production of endothelial derived nitric oxide (EDNO) and augmented levels of reactive oxygen species (ROS). Thus, in this review, we discuss novel therapeutic targets that either upregulate EDNO production or increase antioxidant enzyme capacity in an effort to limit oxidative stress and restore endothelial function. In particular, endogenous signaling molecules that positively modulate EDNO synthesis and mimetics of endogenous antioxidant enzymes will be highlighted. Consequently, manipulation of these unique targets, either alone or in combination, may represent a novel strategy to confer vascular protection, with the ultimate goal of improved outcomes for diabetes-associated vascular complications.